The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Substrate processing systems for performing deposition and/or etching typically include a processing chamber with a pedestal. A substrate such as a semiconductor wafer may be arranged on the pedestal. For example in chemical vapor deposition (CVD) or atomic layer deposition (ALD) processes, a gas mixture including one or more precursors may be introduced into the processing chamber to deposit a film on the substrate or to etch the substrate.
In some substrate processing systems, radio frequency (RF) plasma may be used to activate chemical reactions. Some chemical reactions that happen in the gas phase lead to nucleation, clustering, and/or agglomeration of particles in a reactive volume of the RF plasma. The particles remain suspended in the RF plasma while the RF plasma is on. The particles do not fall onto the substrate due to a balance of forces acting upon the particles. For example, electrostatic repulsion suspends the particles in the RF plasma at a plasma boundary or plasma sheath.
After the RF excitation is turned off, the particles may fall onto the substrate. Therefore, most substrate processing systems evacuate the processing chamber by pumping residual gases for a predetermined period. During the predetermined period, the particles settle down in the processing chamber or are evacuated by the pump.